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I removed my stock airbox/silencer and noticed an imediate improvement in power. Few questions though.
1. Will removing my silencer/airbox froce my mixture to run thin?
2. How should this effect my mileage? and why?
3. Are there any negatives other then a louder engine that I should be worried about?
4. Will this effect emissions? I need to get my smog done soon.

Thanks, I know alot of the questions have easy answers, I just couldn't find them.

seriously, go get some pvc pipe and run it to the fender. the difference in power is very very noticable, i did the exact same thing and you only think you're making power, but you aren't until it gets the colder air.

when i installed my spark plugs the battery was out for about 45 mins(impossible to reach cylinders 2 and 4 without removing it) and without touching the brake pedal or anything it sure as hell reset. just disconnect it and leave it for a while.

when i installed my spark plugs the battery was out for about 45 mins(impossible to reach cylinders 2 and 4 without removing it) and without touching the brake pedal or anything it sure as hell reset. just disconnect it and leave it for a while.

How do you know it reset? I'm telling you from experience it can take a long time for charge to leave the system, even w/ the brake trick.

you will notice a small decrease in mileage, simply because your ecu will correct things for the increased amount of air flowing into the motor, other then that, there aren't any drawbacks

Milage will increase with any modification that allows less vaccum for the same throttle plate position in the throttle body. THe computer putting more fuel into the engine, obviously uses more gas per mile, UNTIL you follow through and figuer out what that means. You are getting more air and fuel into the engine, thus generating more power. More power will make you go faster for the same throttle position. You do not want to go faster, you want to go the same speed, so you use LESS throttle to go ghte same speed. If you have 2 imprezas, the same weight, and the same drag coefficent one with 5 billion horse power one with 125 HP. It doesn't matter which one you drive at 55 MPH, they are going to require the same ammount of HP to the wheels to sustain 55 MPH. With engines with very close brake fuel consumption, they will use the same ammount of fuel to generate that HP needed to sustain a certain velocity.

THe fuel effeciency has nothing to do with horse power, fuel or air in a properly tuned engine. It is all about air entering the engine. With identical engines, the engine with the least amount of "drag" in the intake structure is going to use less engine power to draw air into itself, this power inturn is used for driving the wheels resulting in greater effeciency per volume of fuel.

If you have seen a decrease in milage from mearly an intake, it means your "intake" is junk, or you drive harder to listen to it.

Thanks guys. I'll put in the PVC sometime this week. Any suggestions on easiest ways? Especially with the angle change to reach the filter? Any particular ways to mount it to the fender?

First off you want ABS (black) not PVC (white) pipe. I personally have had good luck with 3 inch, but it is loud and requires modifying of the air box. Since the stock intake size is 2.5 inches, 2.5in ABS pipe with a 30 degree elbow and 2.5in rubber connector should suit you well (version 1 in link below)

Where the ABS goes into the fender, use any old hose; cut a slit down the side and line the circular hole with the hose. This stops most vibrations. I will have pics of this soon.

How do you know it reset? I'm telling you from experience it can take a long time for charge to leave the system, even w/ the brake trick.

because my CEL was cleared. that only happens with a reset. also, the car learned how to mix the newer intake with the cold night air MUCH better than it had, there was noticible power all across the rev range, and it no longer leaned out at higher RPM(at least not as much)

RStoWRX- why ABS instead of PVC? i couldn't find any 2"abs and it's much harder to cut(i have no hack saw, i cut mine with a shoelace... no lie.)

1. 2" is smaller then stock (2.5"), why are you wanting to detune your car? go with 2.5", same as stock but straight, or 3"; huge hp gain in the last 2k rpm(4750-6750), with a small loss of torque under 1500 rpm.

2. Why ABS plastic? PVC releases harmful gasses when heat is applied. ABS is closer to the stock intake material as well. ANY kind of metal intake is bad, it just gets too hot. Thatís why almost no cars have metal intake from the factory.

if i can find some ABS in 2" i'll switch... but for the second time, it's not a downgrade to go from a 2.5" with boxes and turns and baffles and silencers to a 2" straight through pipe. the 2" pipe flows better than the baffle at mid and high rpm.

because my CEL was cleared. that only happens with a reset. also, the car learned how to mix the newer intake with the cold night air MUCH better than it had, there was noticible power all across the rev range, and it no longer leaned out at higher RPM(at least not as much)

You must have a low charge ECU then, ( ) becuase none of the ones I've reset have gone in <25mins.